<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .Box-A {
            width: 100%;
            height: 100px;
            text-align: center;
            font-size: 28px;
            background-color: rgb(253, 246, 227);
        }

        .Box-B {
            display: flex;
            justify-content: space-around;
        }

        .Box1 {
            text-align: center;
            width: 300px;
            height: 100vh;
            background-color: rgb(79, 151, 56);
        }

        .Box2 {
            text-align: center;
            width: 100%;
            height: 100vh;
            background-color: rgb(255, 255, 255);
        }

        .Box3 {
            text-align: center;
            width: 300px;
            height: 100vh;
            background-color: rgb(130, 51, 132);
        }

        @media screen and (max-width:1000px) {
            .Box-B {
                display: flex;
                flex-direction: column;
            }

            .Box1 {
                width: 100%;
                height: 300px;
                order: 2;
            }

            .Box2 {
                width: 100%;
                height: 300px;
                order: 1;
            }

            .Box3 {
                width: 100%;
                height: 300px;
                order: 3;
            }
        }
    </style>
</head>

<body>
    <div class="Box-A">一天到晚游泳的鱼</div>
    <div class="Box-B">
        <div class="Box1">左侧</div>
        <div class="Box2">中间</div>
        <div class="Box3">右侧</div>
    </div>

</body>

</html>